A PCB (Printed Circuit Board) is formed by printing a circuit line pattern on an electrical insulating substrate by using a conductive material such as copper (Cu), and refers to a board right before electronic components are mounted thereon. In other words, the PCB refers to a circuit board in which the mounting positions of the electronic components are determined, and a circuit pattern connecting the electronic components is fixedly printed on a flat plate in order to densely mount electronic devices on the flat plate.
In general, such a PCB is classified into a single-layer PCB and a multi-layer PCB which is a build-up board constructed by stacking PCBs in a multiple layer.
In particular, recently, in order to realize slim and light electronic products, system integration technologies have been required. To this end, technologies of manufacturing an embedded PCB and a cavity PCB have been spotlighted. The embedded PCB has advantages in that components mounted on the surface thereof are completely buried during the PCB process, thereby increasing the degree of freedom in the design of interconnections in the vicinity of the components. However, in the embedded PCB, the compatibility between the embedded components and PCB raw materials and the reworking of defected components are difficult. In addition, the embedded PCB has a limitation in the inspection of the components.
The cavity PCB has disadvantages in that components are not completely buried therein, but installed in a cavity formed in the direction of mounting a chip, so that the degree of freedom in design may be lowered. However, the cavity PCB is very effective in the reworking and inspection of the components that are difficult in the embedded PCB. In addition, although the cavity PCB has been greatly applied to technologies with a mold process scheme based on a LTCC (Low Temperature co-fired ceramic), the cavity PCB has been rarely applied to a PCB requiring a layer-by-layer scheme.
This is because the cavity region cannot exactly be formed, and circuits provided inside the cavity may be damaged in plating, image, and etching processes of a PCB process.
FIGS. 1A and 1B are schematic views showing the process of forming a cavity in the cavity PCB according to the related art.
As shown in FIGS. 1A and 1B, it is very difficult to form a cavity C, in which an electronic device chip is installed, in a PCB having a plurality of circuit patterns 1a, 1b, 2a, 3a, 4a, and 5 formed in multi-layer insulating layers 1, 2, 3, 4, and 5.
In other words, as shown in FIG. 1A, a scheme of selectively forming the cavity C in the PCB having a stack structure in the form of a complete product by using a milling bit M is mainly used. This scheme requires the process precision of 5 μm. However, since the process precision is actually in the range of about 50 μm to about 100 μm, the process for the cavity is very difficult. In addition, since the great difference occurs in the process accuracy, the reliability for a product may be degraded in mass production.